(1) Field of the Invention
The present invention relates to a synthetic pulp having an improved hydrophilic property. More particularly, the present invention relates to a thermoplastic resin synthetic pulp having an excellent wetting property even in the dry state.
Furthermore, the present invention relates to a hydrophilic heat-fusion-bonding synthetic pulp. More specifically, the present invention relates to a hydrophilic heat-fusion-bonding synthetic pulp of a thermoplastic resin, which can partially bond filaments of other fibrous product such as a natural pulp, a natural fiber or a glass fiber by mixing this synthetic pulp with said other fibrous product, forming the mixture into a sheet or other shaped article and subjecting the sheet or the like to a high-temperature heat treatment to melt at least a part of the synthetic pulp, and which has excellent wetting property and hydrophilic property even after the heat-fusion treatment, and also to a fibrous product comprising this synthetic pulp.
(2) Description of the Prior Art
A so-called synthetic pulp formed from a thermoplastic resin as the starting material is known. For example, Japanese Patent Publication No. 47049/77 discloses a process for the preparation of a pulp product which comprises discharging a high-temperature high-pressure dispersion of a polyolefin in a hydrocarbon solvent and water in a reduced pressure zone to effect flash spinning and obtain a dispersion of a polyolefin fibrous substance in water and beating or refining the fibrous substance.
This synthetic pulp is hydrophobic and has no water-absorbing property. It is known that in order to impart wetting and water-absorbing properties to this synthetic pulp, the surface treatment is carried out by incorporating polyvinyl alcohol or non-ionic surface active agent into the synthetic pulp.
However, a polyolefin type synthetic pulp surface-treated with polyvinyl alcohol shows a dispersibility when immersed in water, but in the dry state, the synthetic pulp shows a water-repellent property and does not show a wetting or water-absorbing property.
Moreover, a synthetic pulp surface-treated with a non-ionic surface active agent is defective in that if a surface active agent having a large HLB value is used, although the synthetic pulp has a wetting property, bubbling is violent at the time of wetting, and that if a surface active agent having a small HLB value is used, the wetting property is insufficient.
Furthermore, the synthetic pulp surface-treated with a surface active agent is defective in that if the synthetic pulp is mixed with other fibrous product such as a natural pulp, a natural fiber or glass fiber and subjected to a high-temperature heat treatment to melt the synthetic pulp and partially bond filaments of the fibrous product to one another, the surface active agent adhering to the synthetic pulp is oxidized and decomposed and the hydrophilic property given to the synthetic pulp by the surface treatment with the surface active agent is lost. Even if the non-surface-treated syntheic pulp is mixed with other fibrous product and a product obtained by partially fusion-bonding filaments of the fibrous product to one another through the synthetic pulp is surface-treated with a surface active agent for overcoming the above-mentioned defect, it is difficult to effectively treat only the synthetic pulp.
The foregoing problems are included in not only synthetic pulps as described above but also other various fibrous products of thermoplastic resins.